Gyrinus Geoffroy, 1762

Gustafson, Grey T. & Short, Andrew E. Z., 2017, Review of the whirligig beetle genus Gyrinus of Venezuela (Coleoptera: Gyrinidae), Acta Entomologica Musei Nationalis Pragae 57 (2), pp. 479-520 : 481-482

Subgenera of Gyrinus Geoffroy, 1762

The genus Gyrinus was first divided into formal subgenera by ZAITZEV (1907), who separated Gyrinus minutus Fabricius, 1775 into the subgenus Gyrinulus , based on the presence of a small carina at the base of the scutellar shield and a mesoventrite with a strong medial groove. HATCH (1926) was next to divide Gyrinus , erecting the subgenus Neogyrinus for five Neotropical species having the medial elytral striae effaced (e.g. Figs 1–6 ) and lacking a basal carina on the scutellar shield, with G. chalybaeus Perty, 1830 selected as the type. The final division of the genus was originally proposed by OCHS (1935a) to separate species having the pronotum strongly sculptured ( Figs 38–39 ) and the lateral elytral striae sulcate with more strongly impressed punctures ( Figs 43, 45 ) to the subgenus Oreogyrinus Ochs, 1935 . OCHS (1949) later providedmore diagnostic featuresof members of Oreogyrinus : pronotaltransverse medialdepression or creasealways present ( Figs 38–39 ); elytralstria XI strictlymarginal ( Figs 40–41 ); elytral lateral margin strongly riffled and terminated in an apical plica ( Figs 40–41 ); venter darkly colored, with only the mesoventrite, epipleura, and anal segment reddish in color. OCHS (1935a) selected G. parcus Say, 1830 as the type for the subgenus, which is one of the most widely distributed Gyrinus species in the New World ( OYGUR & WOLFE 1991), being found from southern South America to North Dakota. Despite the species selected for the type, OCHS (1935a) emphasized that members were primarily found along the Andes and mountain chains of Central America ( OCHS 1949).

In particular, the distinction between Oreogyrinus and the nominotypical subgenus has become more difficult with the discovery of a lowland Amazonian species, G. fittkaui Ochs, 1963 , resembling G. marinus Gyllenhal, 1808 and lacking many diagnostic features of an Oreogyrinus . We here report on the discovery of a new Amazonian species lacking nearly all diagnostic features of an Oreogyrinus , further weakening its distinction from the nominotypical subgenus (see discussion under Gyrinus iridinus sp. nov.). The characters separating Neogyrinus from Gyrinulus have also been called into question ( OCHS 1967b). However, Neogyrinus is quite distinct from both Oreogyrinus and nominotypical Gyrinus members. The features of Neogyrinus are distinct enough that full generic rank has been proposed ( CRESPO 1986). However, CRESPO’ s (1986) decision was based primarily on the form of the anal hooks of the third instar larva of G. ovatus . As this is a very minor feature, and one not examined in any other Neogyrinus species , we do not follow CRESPO’ s (1986) proposed change in rank.

OYGUR & WOLFE (1991) introduced a novel character for Gyrinus taxonomy, the metanepisternal ostiole, which in combination with the classical characters, appears to distinctly separate Neogyrinus from Oreogyrinus , Gyrinulus and Gyrinus s. str. Members of Neogyrinus always lack a metanepisternal ostiole, while the vastmajority of species in the other subgenera possess a metanepisternal ostiole, even if it is small (as in the Oreogyrinus species treated here). The additional subgeneric characters will make readily apparent species of the nominotypical subgenus that have lost the metanipsternal ostiole (e.g. Gyrinus rugosus Oygur & Wolfe, 1991 and G. gibber LeConte, 1868 ).

As the monophyly of the subgenera has yet to be tested phylogenetically, given the considerable differences between Neogyrinus species when compared to members of Oreogyrinus and the nominotypical subgenus, and the utility of subgenera to quickly convey this information, we here continue to use the classical subgenera when treating Neotropical species.

Figures

Figs 1–6. Dorsal habitus of Neogyrinus species, scale bar = 1 mm. 1 – Gyrinus sabanensis sp. nov. 2 – G. gibbus Aubé, 1838 from Amazonian Venezuela. 3 – G. ovatus Aubé, 1838. 4 – G. guianus Ochs, 1935. 5 – G. gibbus ‘var. apicalis’ Sharp, 1877 from Caracas valley, Venezuela. 6 – G. rozei Ochs, 1953.

Figs 33–38.Dorsal habitus of Oreogyrinus species, scale bar = 1 mm. 33 – Gyrinus venezolensis Ochs, 1953, female. 34 – G. venezolensis, male. 35 – G. vinolentus sp. nov. female. 36 – G. vinolentus, male. 37 – G. iridinus sp. nov., female paratype. 38 – G. iridinus, male holotype.

Figs 39–40. SEM images of the pronotum showing sculpturing of wrinkles and riffles of the lateral margins, arrows indicate pronotal transverse crease. 39 – Gyrinus venezolensis Ochs, 1953. 40 – G. vinolentus sp. nov.

Figs 43–46. SEM images of elytral interval reticulation and strial punctures. 43–44 – Gyrinus venezolensis Ochs, 1953. 43 – intervals II and III, striae I–III. 44 – intervals IX and X, striae VIII–X. 45–46 – G. vinolentus sp. nov. 45 – intervals II and III, striae I–III. 46 – intervals IX and X, striae VIII–X.

Figs 41–42. SEM images of the elytron of Oreogyrinus species, scale bars = 1mm, arrows indicate the pre-apical swelling interrupting the elytral lateral margin. 41 – Gyrinus venezolensis Ochs, 1953. 42 – G. vinolentus sp. nov.